Remove var not used.

tests/server/sockfilt.c

@@ -170,7 +170,6 @@ static int juggle(curl_socket_t *sockfdp,
   fd_set fds_err;
   curl_socket_t maxfd;
   ssize_t r;
-  int err;
   unsigned char buffer[256]; /* FIX: bigger buffer */
   char data[256];
   curl_socket_t sockfd;